The metering rods basically control the fuel flow through the jets at idle and come in more sizes than I can remember. They are mounted on a spring loaded arm above the jets. If you could post a picture if the carb it would help. I've messed with a few AFB's and it's my understanding that Thermo Quads aren't much different. Edelbrock bought out Carter a few years back and their carbs are updated AFB's.